The long term objective is to develop a new technology for industry scale affinity separations employing proprietary Bio-Receptor Ferrofluids (BR- FF) in combination with existing High Gradient Magnetic Separators (HGMS) and improved systems currently being developed. BR-FF are being used successfully for doing immunoassays and together they represent a significant step forward in the field offering numerous advantages over prior systems. the specific aims of this proposal are to determine if BR- FF as currently synthesized or as synthesized by relatively straightforward modification can withstand the rigors of desorption (low pH, denaturants, chaotropic ions) and recycling. Affinity separations currently play a minor role in bioprocessing, in part because of cost and the nature of affinity supports (particles or membranes) which are constrained to batch mode and ultra-clean solutions. BR-FF and HGMS offers the potential for continuous affinity separation which can function in the presence of major solution contaminents including solids; thus a new bioprocessing technology which also requires significantly fewer processing steps possible.